SpaceX has delayed its most secretive mission yet — codenamed Zuma — yet again. This time, the delay is as unusual as the mission itself.

The aerospace company has been trying to launch Zuma on behalf of the U.S. government since mid-November, but a string of setbacks have kept the mission from taking off. On Thursday, SpaceX announced on Twitter that it would not be launching Zuma on Friday as planned due to “extreme weather” in Florida. SpaceX is now eyeing Sunday for launch.

Team at the Cape completed additional propellant loading tests today. Extreme weather slowed operations but Falcon 9 and the Zuma spacecraft are healthy and go for launch—now targeting January 7 from Pad 40 in Florida.

Florida, home of the Kennedy Space Center, has been experiencing an unusual cold snap over the last week. CBS reports that some parts of south Florida dipped below 40 degrees, causing frozen iguanas to fall out of trees. This week, Cape Canaveral, where SpaceX’s Falcon 9 rocket for Zuma will launch from, dipped as low as 46 degrees.

Since the Zuma mission deals with highly classified information, there’s not a lot we know about it. It’s unclear what government agency is sending up the satellite, for example. As Inverse previously reported, all we know is that the payload was designed by defense technology company Northrop Grumman and that at some point, it’ll fly atop a Falcon 9 rocket into low earth orbit.

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Probably the most public information about Zuma is how many times it’s been delayed. In November, SpaceX attributed the setbacks to various testing issues, in addition to “tak[ing] a closer look at data” from another customer.

Standing down on Zuma mission to take a closer look at data from recent fairing testing for another customer.